cmsaf (version 1.9.5)

levbox_mergetime: Function to combine NetCDF files and simultaneously cut a region and level.

Description

This function selects a region and a level from a bunch of layered CM SAF NetCDF files that match the same pattern of the filename, and writes the output to a new file. If no longitude and latitude values are given, files are only merged. All input files have to have the same rectangular grid, level and variable. The reference time of the output file is determined by the first input file.

Usage

levbox_mergetime(var,level,path,pattern,outfile,lon1,lon2,lat1,lat2,nc34)

Arguments

var

Name of NetCDF variable (character).

level

Number of level that should be extracted (integer).

path

The directory of input NetCDF files without / at the end (character).

pattern

A part of the filename, which is the same for all desired input files (character).

outfile

Filename of output NetCDF file. This may include the directory (character).

lon1

Longitude of lower left corner (numeric).

lon2

Longitude of upper right corner (numeric).

lat1

Latitude of lower left corner (numeric).

lat2

Latitude of upper right corner (numeric).

nc34

NetCDF version of output file. If nc34=4 the output file will be in NetCDFv4 format (numeric). Default output is NetCDFv3.

Value

A NetCDF file including the merged timeseries of the selected region is written. The output NetCDF file contains only the selected level.

Examples

# NOT RUN {
## Create an example NetCDF file with a similar structure
## as used by CM SAF. The file is created with the ncdf4 package.
## Alternatively example data can be freely downloaded here: 
## <https://wui.cmsaf.eu/>

library(ncdf4)

## create some (non-realistic) example data

  lon <- seq(5,15,0.5)
  lat <- seq(45,55,0.5)
  time <- c(as.Date('2000-01-01'), as.Date('2001-02-01'))
  origin <- as.Date('1983-01-01 00:00:00')
  time <- as.numeric(difftime(time,origin,units='hour'))
  level <- c(1:5)
  data1 <- array(250:350,dim=c(21,21,5,1))
  data2 <- array(230:320,dim=c(21,21,5,1))

## create two example NetCDF files

   x <- ncdim_def(name='lon',units='degrees_east',vals=lon)
   y <- ncdim_def(name='lat',units='degrees_north',vals=lat)
   l <- ncdim_def(name='level',units='1',vals=level)
   t <- ncdim_def(name='time',units='hours since 1983-01-01 00:00:00',
   vals=time[1],unlim=TRUE)
   var1 <- ncvar_def('SIS','W m-2',list(x,y,l,t),-1,prec='short')
   vars <- list(var1)
   ncnew <- nc_create('CMSAF_example_file_n1.nc',vars)
   ncvar_put(ncnew,var1,data1)
   ncatt_put(ncnew,'lon','standard_name','longitude',prec='text')
   ncatt_put(ncnew,'lat','standard_name','latitude',prec='text')
   ncatt_put(ncnew,'level','standard_name','level',prec='text')
   nc_close(ncnew)

   t <- ncdim_def(name='time',units='hours since 1983-01-01 00:00:00',
   vals=time[2],unlim=TRUE)
   ncnew <- nc_create('CMSAF_example_file_n2.nc',vars)
   ncvar_put(ncnew,var1,data2)
   ncatt_put(ncnew,'lon','standard_name','longitude',prec='text')
   ncatt_put(ncnew,'lat','standard_name','latitude',prec='text')
   ncatt_put(ncnew,'level','standard_name','level',prec='text')
   nc_close(ncnew)

## Cut a region and levl, and merge both example CM SAF NetCDF files 
## into one output file. First get path information of working directory.
   wd <- getwd()
   levbox_mergetime('SIS',1,wd,'CMSAF_example_file_n',
   'CMSAF_example_file_box_mergetime.nc',8,12,48,52)
# }